Prothonotary Warbler

Wednesday, 27 August 2014

Tallgrass prairies of Walpole, in their prime

I have been fascinated by prairie and savanna from at least as far back as 1973, when I was working at Rondeau. And since the 1980s, I have had the privilege to be able to explore some of the finest tallgrass prairie and oak savanna in Ontario, and arguably Canada. The prairies of the Walpole Island First Nation are indeed remarkable and spectacular. One of the prairie sites has, on more than one occasion, hosted a breeding pair of Henslow's Sparrows!

You may remember a previous post, in early July, where I was able to visit one of the more remote prairies at Walpole Island, along with the owner and her family. It looked like this:

I had memories of this site from a few years earlier, when it was in its peak of colour with the Dense Blazing-star in its prime, along with several other showy species, so we planned to re-visit in early August to again see it in that showy condition. On the way in, we saw various prairie flowers in their prime, including Flowering Spurge.

Flowering Spurge (Euphorbia corollata)

Grey-headed Coneflower was also doing well. It is provincially ranked as S3, meaning there are fewer than 80 locations for it in Ontario and is vulnerable to extirpation..

Gray-headed Coneflower (Ratibida pinnata)

As we got to the site we were headed for, we were not disappointed.

This image was taken from a very similar vantage point as the first one in this post, but at a slightly different angle.

Dense Blazing-star (Liatris spicata) is one of the prairie plant species which many consider to be iconic.....that is, when one sees it, it evokes a sense of place that is a high quality tallgrass prairie. Mind you it can grow in some rather disturbed sites as well, but in a setting such as the one above with a multitude of other quality prairie species, it truly is an indication of a special place. Dense Blazing-star is a Threatened species under the Endangered Species Act. Under the Provincial Ranking system, it is S3.

Purple is the primary colour, but if you look closely at the image preceding this, you may have noticed a white plant. It is a rare white colour form; less than one per cent of all blazing-star stems are white. It serves to add to the diversity of colour at this time of year when so many prairie plants are purple against a green background.

On the day of our visit, it was a wonderful day to see some butterflies as well. Monarchs, Red-spotted Purples and Black Swallowtails were fairly abundant, but the one that caught my eye was Giant Swallowtail. There were several flitting about, enjoying the nectar of the rich purples available to them in this setting. Giant Swallowtails are ranked as S2 in the provincial ranking system, meaning that there are likely fewer than 20 populations and have a restricted range in Ontario and are very vulnerable to extirpation.

In both of these cases, the swallowtails chose to sip on the flowers of an ironweed rather than the blazing-star and that seemed to be the case most of the time. I'm not sure if the deeper purple colour was more attractive, or maybe the nectar was more satisfying. I'm not a butterfly whisperer to know that detail.

There are two species of ironweed on the Ontario prairies. For many years it was believed there was just one species, but in the early 1990s while a botanical colleague and I were photographing some prairie plants on Walpole, he realized there was something different about some, and after a closer examination of images and confirming using technical manuals, I concurred, thus adding with some certainty that there was in fact another species. The differences are somewhat subtle, and are based in part on the number of florets (small, individual flowers on the flower head). One species is Tall Ironweed and the other is Missouri Ironweed. The next photo is of the latter, and most recently confirmed, species. It is provincially ranked as S3.

Missouri Ironweed (Vernonia missurica)

Of course tallgrass prairies are more than just colourful wildflowers, although they are the showier plants. But as the name 'tallgrass' suggests, grasses are a major component of such a prairie. A healthy prairie in the mid-west consists of about 70% grasses, although there are only a handful of species making up that ~70%. Here in the eastern range of the tallgrass prairie biome, it is believed that wildflowers, collectively called 'forbs', make up about 50% of the vegetation in a healthy prairie, and grasses the other 50%. This may be due in part to the greater amount of precipitation in the east. Prairie grasses in general have deeper root systems than most forb species, so that in the drier part of the prairie range in the mid-west, the grasses have the advantage over the forbs. It may also be partly due to the greater presence of savanna, those prairie-type habitats where up to 25% of the cover is made up of fire resistant trees, usually oak species. Some forbs that do well in an oak savanna will also do well in a tallgrass prairie.

Indian Grass (Sorghastrum nutans) is one of the main grasses to be found on a tallgrass prairie. Grasses have flowers too, although most people do not pay much attention to them. This particular plant was in good flower, with the bright yellow stamens visible here.

In this next photo, there are some tall grasses visible amongst the forbs, although more in the background. They are Big Bluestem (Andropogon gerardii), a.k.a. Turkeyfoot, named because of the 3-4 flower and seed spikes at the top that may resemble the foot of a turkey. It is by far the most abundant grass of most tallgrass prairies.

Also in this image is a Tall Sunflower (Helianthus gigantea) visible in the upper right. In a few days, this scene will have taken on a decidedly yellow look, as the many goldenrod species open up. There are some goldenrods in this image that are in a tight bud stage, but have not yet opened.